5 Answers

kk stands for okey-doke or okey-dokey (in The Macquarie Dictionary 3rd ed, both versions are given, and it's a rhyming reduplication of 'okay' meaning: "yes; all right"). It's a short form of acknowledging a communication to you (especially texts). And it's quick! In other words, to ensure the person who sent you a message knows you received it, a quick "kk" back to them let's them know you have received their message and all's well. As The Macquarie Dictionary is Australian, maybe it's an Australianism.